swift performSegueWithIdentifier sender value

Question

I am trying to understand how the sender value works in segues.

In some places in my code both works:

performSegueWithIdentifier("mySegue", sender: self)

performSegueWithIdentifier("mySegue", sender: sender)

But what is the difference between having self / sender?

Answer 1

As @iosDev82 says in his answer, sender is an optional that names the object (if any) that triggered the segue.

If you trigger a segue through code in a view controller, you could pass the view controller (self), or you could pass nil. It's just a piece of information that is passed along to prepareForSegue (again as iOSDv82 says.)

If you trigger a segue in the code of an IBAction method, your IBAction may have it's own sender parameter (frequently a button.) In that case you can pass along the sender parameter to the performSegueWithIdentifier method.

Example:

@IBAction func buttonAction(sender: UIButton)
{
  //In this case the button IBAction takes a pointer to the button as a param.
  //Pass it on to the segue in case performWithSegue needs it. 
  self.performSegueWithIdentifier("someID", sender: sender)
}

Answer 2

sender is just an argument that gets passed along with this function.

This is received later in the function prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) , where you can get this object and make decision based on who the sender is.

Answer 3

As an Example, suppose you want to edit something at an IndexPath . You call

performSegue(withIdentifier: "showItem", sender: indexPath)

from wherever you want ( indexPath is of type IndexPath here).

Then, inside the prepare(segue:sender:) , you do:

...
switch segue.identifier {
case "showItem"?:
     // Figure out which row was just tapped
     if let row = tableView.indexPathForSelectedRow?.row {
         editRow(segue, row)
     } else {
         let selectedIndexPath = sender as! IndexPath
         editRow(segue, selectedIndexPath.row)
     }
...